You can use any size SD card in a camera, irrespective of the maximum number of megapixels. (That, of course, assumes that the camera uses SD cards and not some other type of removable media!).
Unless you intend to enlarge prints to bigger than A4 size, you don't need 7Mp. Above about 3Mp, you won't notice any difference in the quality of printed images at A4 size. (All you'll get is bigger files taking up more space on the memory card). You'd be better off spending your money on a camera with a decent optical zoom. (8x to 12x). For most users, this is far more useful than having lots of Mp you don't need.
Chris